"""
19. Remove Nth Node From End of List (Medium)

Given a linked list, \
remove the n-th node from the end of list and return its head.

Example:

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, \
the linked list becomes 1->2->3->5.
Note:
Given n will always be valid.

Follow up:
Could you do this in one pass?

"""


# Definition for singly-linked list.
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None


class Solution:
    def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
        fast = head
        while n > 0:
            fast = fast.next
            n -= 1
        if fast is None:
            return head.next
        slow = head
        while fast.next is not None:
            slow = slow.next
            fast = fast.next
        slow.next = slow.next.next
        return head
